1. Field
The present invention relates to a cooling system for cooling a heat-generating unit, and more particularly relates to a cooling system for cooling a semiconductor device mounted on a printed circuit board, and to a projection-type image display apparatus using the same.
2. Description of the Related Art
Recently, the amount of heat released from semiconductor devices mounted on printed circuit boards has been increasing, and a technology for cooling the semiconductor devices has become more and more important.
In particular, the processing clock speed of CPUs for use in information processing devices, such as personal computers, etc., has been rapidly moving toward higher frequencies in recent years so as to realize faster processing speeds.
Along with the higher frequency trend of the processing clock of CPUs, the amount of heat released from CPUs is rapidly increasing, and a technology for cooling CPUs has become indispensable to maintain CPU performance.
In many cases, to cool a CPU, a method is employed in which a radiator (sometimes called a heat sink) provided with numerous radiating fins or numerous radiating projections is thermally connected to a heat-generating portion of the CPU, and the radiator is forcibly air-cooled.
When the radiator is attached to the CPU, a mechanical connection between the radiator and the CPU has to be maintained even when vibration or a shock is applied thereto, while the heat transfer performance between the radiator and the heat-generating portion of the CPU has to be secured.
In addition, in recent years, there is a trend in key electronic devices, such as CPUs and the like toward an easily exchangeable method using a socket or the like, instead of the method of directly fixing the electronic device to a printed circuit board with a soldered connection. In response to the above-mentioned trend, an easy method for attaching the radiator to the CPU or detaching the radiator from the CPU is required.
Technologies for securing a thermal connection and a mechanical connection for the semiconductor device, for example, connecting a CPU and the like with a radiator, in which both the semiconductor device and CPU and the like can easily be attached and detached, are disclosed in Jpn Pat. Publication No. 2001-230356, Jpn Pat. Publication No. 10-4161, and Jpn pat. Publication No. 8-46097.
However, the main technologies disclosed in all of these documents use a method in which the radiator is fixed by using an appropriate member from above.
For example, in the technology disclosed in Jpn Pat. Publication No. 2001-230356, a radiator is placed on a CPU that is attached to a socket provided on a printed circuit board, and is fixed to the CPU by downwardly pressing the radiator and the CPU toward the socket with metal wire rods having elasticity in engagement with two positions of the socket.
A concave portion is provided at the center of the radiating fins of the radiator, so as to prevent the metal wire rods from deviating at an upper part of the radiator.
Even though the mechanical connection and the thermal connection of the CPU with the radiator are secured by the above-mentioned configuration, radiating performance is sacrificed. This is because the concave portion is formed at the center of the radiating fins and the radiating area of the radiating fins is thereby reduced.
In Jpn Pat. Publication No. 10-4161, a technology for fixing the radiator and the CPU from above the radiator using metal wire rods having elasticity or a plate spring is disclosed, like that disclosed in Jpn Pat. Publication No. 2001-230356. The radiator disclosed in Jpn Pat. Publication No. 10-4161 is provided with numerous radiating projections, and the metal wire rods and the plate spring are provided for pressing the radiator and the CPU downward fitting into the predetermined clearance of the numerous radiating projections.
The shape of a radiating portion described in Jpn Pat. Publication No. 10-4161 is limited to a projecting shape, and an embodiment describing a radiator provided with plate-shaped radiating fins is not disclosed therein. In addition, in the case of forcibly air-cooling the radiator, the air resistance of a flowing path for air is expected to be increased due to attached members, such as the metal wire rods, the plate spring, and the like.
In Jpn Pat. Publication No. 8-46097, a technology for fixing the CPU and the radiator by pressing down a plate-shaped member from above is disclosed. In this technology, the CPU is covered with the radiator, and the plate-shaped member further covers the radiator from above.
Even in the technology disclosed in Jpn Pat. Publication No. 8-46097, the radiating area of the radiating portion is partially sacrificed by a boss portion and the like for fixing the radiator and the plate-shaped member.
Thus, all of the cooling systems disclosed in the above-mentioned patent applications use a method to fix the radiator with the CPU from above, and therefore, the cooling system is configured such that some of the cooling performance is sacrificed due to a decrease of the radiating area, or an increase of the air resistance of the flowing path due to the provision of the fixing members.
On the other hand, semiconductor devices that require forcible cooling are not limited to the technical field of information processing apparatuses.
In the technical field of a projection-type image display apparatus, a key electronic device, which is called a display device, is required to be cooled to the same extent as CPUs, or even greater.
Display devices include a transmissive liquid crystal display devices and reflective liquid crystal display devices, and the projection-type image display apparatus using the liquid crystal display device is sometimes called a liquid crystal projector.
A DMD (Digital Micro-Mirror Device: trademark) is a known display device other than those described above, and a projection-type image display apparatus using the DMD is called a DLP (Digital Light Processing: trademark) type projector.
The DMD is a reflection-type display device formed of microscopic mirrors on a surface thereof that correspond in number with pixels, and light falling on a surface of the DMD is modulated and reflected by electronically and mechanically changing an angle of each of the mirrors.
Both DMD (trademark) and DLP (trademark) are trademarks of Texas Instruments in the United States of America.
Both the above-mentioned liquid crystal display and DMD control image signals pixel by pixel using a semiconductor element and heat is generated by the semiconductor element itself.
Further, the above-mentioned display devices project reflection light or transmission light onto a screen by reflecting or transmitting light from a light source that is housed in the projection-type image display apparatus. When the light is projected, a certain reflection loss or transmission loss occurs in the display device, and as a result, some of the light energy is converted into heat energy.
Therefore, in the liquid crystal display device and the display devices such as the DMD and the like, heat generation caused by the reflection loss and the transmission loss is added to the heat generation caused by the semiconductor element itself.